金基中低温钎料的研究现状与展望

Research Status and Prospect of Au-based Medium-Low Temperature Filler Metals

随着电子封装技术的发展以及无铅化进程的推进,目前已开发了诸多无铅钎料合金体系用于代替Sn-Pb钎料,但在熔化温度为280~400 ℃之间的无铅钎料封装领域,价格高昂的Au-Sn、Au-Si、Au-Ge等金基低温钎料是唯一可代替高温Sn-Pb钎料的合金体系,并凭借其优良的钎焊性能被广泛应用于电子封装等领域。然而,随着电子器件高集成度、高功率化发展,熔点低于400 ℃的金基低温钎料已不能完全满足封装要求,亟需开发熔点在400~600 ℃之间的中温钎料。目前,熔化温度在280~600 ℃之间的金基钎料合金体系是高温电子封装的主要选择,甚至部分钎料是唯一的选择。金基钎料虽然具有优良的电导率、热导率、耐腐蚀性能、力学性能和高可靠性等优点,但由于组成相具有高脆性而难以加工成型,加工难度大、成品率低、产品性能差等严重影响了钎料的使用。此外,金基钎料中Au含量普遍较高,使用成本高昂。因此,一直以来除了研究金基钎料的加工工艺外,研究者们在采用合金元素替代Au元素以及开发新的金基合金体系等方面进行了大量探索。针对金基钎料高脆性、难加工的特点,研究人员开发了铸造拉拔轧制法、叠层冷轧法、甩带快速凝固法与电镀沉积法等制备方法,实现了厚度为0.1 mm以下箔材的生产。合金元素对金基钎料的影响研究表明,低熔点合金元素(如Sn、Sb、In等)能降低Au-Ge钎料的熔点,少量Sb的添加还能增强Au-Ge钎料的延展性能,Sb与Sn还能抑制钎焊界面反应层的过度生长。在诸多的金基合金体系中,Au-Ag-Si、Au-Ag-Ge、Au-In、Au-Ga等合金体系作为潜在的新型金基中温钎料得到了关注。这些钎料合金因具有高脆性而无法采用常规方法进行加工成型;同时也因具有优异的润湿铺展性能和良好的力学性能而易于推广应用。本文归纳了金基中低温钎料的研究现状,对金基中低温钎料的性能、特点、应用领域以及合金元素影响等进行了介绍,概述了高脆性中低温金基钎料的各种加工方法及其优缺点,重点分析并比较了Au-Ag系、Au-In系与Au-Ga系中温钎料的性能特征。最后,在评述和归纳现有文献的基础上,对金基中低温钎料的发展方向进行了展望。

As fast development of electronic packaging technology and the inevitable trend of lead-free soldering,a number of alloys have been proposed as alternative Pb-free solders,but in the field of microelectronic and optoelectronic packages,high priced Au-based solder (such as Au-Sn,Au-Si,Au-Ge) is considered as the best one to substitute for high-Pb solders due to their excellent comprehensive properties.However,with the development of high-integration and high-power electronic devices,Au-based low-temperature solders with melting point below 400 ℃ can not fully meet the packaging requirements.It is urgent to develop mid-temperature filler metals with melting point between 400 ℃ and 600 ℃.At pre- sent,among all filler metals with melting points in the range of 280-600 ℃,Au-based alloy systems are the main choice for high-temperature bonding applications in the electronic packaging,or even the only choice. Au-based filler metals have superior resistance to corrosion,high electrical and thermal conductivity,excellent mechanical strength and high reliability,while they are difficult to be processed due to their high brittleness.Processing difficulty,low yield and poor product performance seriously affect the application of Au-based solders.What's more,the Au content in Au-based alloys is generally so high that the use-cost of Au-based solders is high.Therefore,researchers not only studied the processing technology of brittle solders,but also made a lot of explorations in replacing Au with alloying elements and developing new Au-based alloy systems. The casting drawing and rolling method,laminate-rolling process,roll rapid solidification method and the electroplating deposition method were developed to solve the processing problem caused by the high brittleness of the Au-based alloys.Alloy foils with thickness less than 0.1 mm can be worked out by means of using these processes.The effect of alloying elements on Au-based solders shows that low melting point alloying elements (e.g.Sn,Sb,In) can reduce the melting point of Au-Ge solder,and the ductility of Au-Ge solder is enhanced by adding a small amount of Sb.Sb and Sn can also inhibit excessive growth of interfacial reaction layer.Among many gold-based alloy systems,alloys like Au-Ag-Si,Au-Ag-Ge,Au-In,and Au-Ga have been proposed as medium-temperature solders.Although these alloys are brittle and cannot be processed by conventional methods,they have great potential for being widely used in advanced electronic packaging owing to their excellent wettability and good mechanical properties. This review offers a retrospection of the research efforts with respect to Au-based medium-low temperature filler metals.The properties,characteristics,application fields and influence of alloying elements of Au-based medium-low temperature filler metals are introduced.The various processing methods and their advantages and disadvantages of high-brittle Au-based medium-low temperature filler metals are summarized.The performance and characteristics of Au-Ag,Au-In and Au-Ga medium-temperature filler metals are analyzed and compared emphatically.Based on the existing literature,the development direction of Au-based medium-low temperature filler metals is predicted.